1. Field of the Invention
The present invention relates to a blue organic light emitting device having enhanced current efficiency, including: a substrate; a first electrode formed on the substrate; a hole transport layer formed on the first electrode; a blue light emitting layer formed on the hole transport layer; an electron transport layer formed on the blue light emitting layer; and a second electrode formed on the electron transport layer, wherein the electron transport layer includes a material having an energy gap of 2.8 eV or more between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).
2. Description of the Related Art
Light emitting diodes are self-emission type devices. Light emitting diodes have wide viewing angles, high contrast ratios, and short response speeds.
Light emitting diodes can be categorized into inorganic light emitting diodes and organic light emitting diodes (OLEDs) according to the material that is used to form the light emitting layer. OLEDs have higher brightness, lower operating voltages, and shorter response speeds than inorganic light emitting diodes, and can realize many colors.
A conventional OLED includes an anode formed on a substrate, and a hole transport layer, a light emitting layer, an electron transport layer and a cathode are sequentially formed, in this order, on the anode. The hole transport layer, the light emitting layer and the electron transport layer are organic thin films formed of an organic material.
An OLED having the structure as described above has the following driving principle.
When a voltage is applied between the anode and the cathode, holes injected from the anode move toward the light emitting layer through the hole transport layer and electrons injected from the cathode move toward the light emitting layer through the electron transport layer. The holes and electrons, which are also called carriers, are recombined in the light emitting layer and form excitons. The excitons are changed from an excitation state into the ground state, and thus, fluorescent molecules of the light emitting layer emit light.
Green light emitting materials have very high luminescent efficiencies compared to red or blue light emitting materials. Accordingly, development of conventional devices has been focused on green light emission. Thus, conventionally, the energy level of the electron transport layer forming material is adjusted to optimize light emission for a green light emitting layer. In other words, the energy level of the electron transport layer forming material is optimized for green light emitting devices. Accordingly, when an organic layer forming material that is optimized for the energy level of a green light emitting layer is used in blue light emitting devices, the efficiency of the blue light emitting devices will be low compared to the efficiency of green light emitting devices.
To improve the luminescent efficiency of blue light emitting devices, there is a need to adjust the energy level of the electron transport layer forming material to be suitable for a blue light emitting layer.
Most conventional techniques for improving the luminescent efficiency of blue light emitting devices relate to the synthesis of novel compounds, and solutions for improving the luminescent efficiency of blue light emitting devices have not yet been found.